Color photography



-June 24, 1941. H, KUDAR COLOR PHOTOGRAPHY Filed oct. 27. 1939 .NWW/

Patented `lune 24. 1941 COLOR PHOTOGRAPHY Hans Kudar, Berlin-Schoneberg,Germany Application October 27, 1939, Serial No. 301,661

In Germany July 18, 1935 7 Claims.

This invention relates to a method oi color photography, moreparticularly color cinematography, and to a plate or nlm for carryingout said method.

Lenticular nlms are used for pictures in natural colors in such mannerthat by means of each embossed lens, the images of three filter stripesare projected upon the light sensitive emulsion.' However, there arediinculties in printing such images which are partly caused by theincompleteness of the'image of a picture ele' ment of the nrst nlm on anyembossed. lens of the second nlm. Another difnculty lies in that' nlmswith an embossed lens formation require a particularly strong lightsource when projected. Because of these diniculties in printing, andlarge absorption of light by the color filters, attempts have been madeto produce subtractive color printings from pictures made on nlms withan embossed lens formation. To this end, it has been proposed to makethe three-color picture by using a nlm having an embossed lensformation, only for two colors, for example, blue and green, and to usea second separate nlm for the third color, this second nlm touching therst nlm with its emulsion side, and the two nlms together permitting theproduction of subtractive three-color prints. However, subtractivethreecolor pictures can hardly reach the quality of the additivereproduction of colors, since the absozption spectra of the subsequentthree-color layers merge into one another, distortions of color beingcaused thereby.

An object of this invention is to produce a method of color. photographywhich combines the advantages of high projection eniciency obtained bysubtractive color reproduction, with the advantage oi true colorprojection obtained by the additive mixing of the colors.

Another object of the invention is to employ a lenticular nlm for thereproduction of at least three colors.

Another object of the invention is to produce 'a .method of colorphotography in which at least four colors are subtractively recordedupon a nlm, and are additively projected from said nlm.

Another object or the invention is to produce in color photography amore accurate reproduction of natural colors by increasing the spectralrange of a photographic nlm.

According to the invention the production upon a nlm of component imagesin four colors, which permits a simple projection from the nlm of thecomposite image in its natural colors, is obtained by using incombination with a two-color filter,

a lenticular film having two light-sensitive layers lying behind oneanother, and which are sensitized for complementary colors, and a nlterlayer between them which is transparent only for the colors for whichthe light-sensitive layer lying behind it is sensitive.

This invention enables the life-like reproduction of colors beyond thelimits of efficiency of the known three-color photography. Theinadequacy ofA the known color reproduction by component images in threecolors is particularly noticed with whitish colors, and with colors ofcomplicated spectral structure. rlhe well known cause for this dinicultylies in the impossibility of reproducing photographically themonochromatic colors of the spectrum unless a great number of colorcomponents be used. 'I'he color reproduction is much more -perfect ifnot three, but four color components are used. However, the additiveprojection of four colors which would involve complicated technicalprovisions is avoided by the method of this invention,

This application is a continuation-in-part of co-pending applicationSerial No. 91,401, filed July 18, 1936. The present application gives a:more detailed description of color examples than was disclosed in theprior application.

rI'he invention is more fully described with reference to theaccompanying drawing, in which:

Fig. 1 is a now diagram illustrating the various steps in exposing,developing, and projecting the nlm.

Fig. 2 is a diagram illustrating the range of the visible spectrum forwhich various portions of the nlm are sensitized.

Fig. 3 is a diagram illustrating the application of light in thespectrum ranges I and IV of Fig. 2 applied to the nlm.

Fig. 4 is a view similar to Fig. 3, but illustrating light from rangesII and Ill applied to the nlm.

Fig. 5 is a diagrammatic view illustrating the production of four-colorphotographs; and

Fig-6 is a view similar to Fig. 5, but relating to the production ofthree-color photographs.

In Fig. 1 the general process is illustrated diagrammatically. The lightrays from the object to be photographed are passed through a filter anda lens, and impinge upon a lenticular nlm, within which the colors areseparated according to a predetermined plan. The nlm is then developed,which includes the washing of the negative and the coloring of theexposed portions thereon with colors complementary to those which causedsuch developed portions. When the thus prepared nlm is projected, lightemitted from the light source passes first through the colored film,then through a lter similar to that used when the film was exposed, andimpinges upon a screen to reproduce the object in colors.

'I'he lenticular nlm used in the method of this invention carries on itssmooth side a light-sensitive emulsion, the light sensitiveness of whichvis limited, for instance, to the short-wave part divided in order toobtain the colors for which the film is sensitized. Range I includes thewave lengths from 625 to 700ml., range II the wave lengths from 550 to625ML, range III the wave lengths from 475 to 550W, and range IV thewave lengths from 400 to 475ML. One-half of the filter is transparentfor the colors I and IV, for example, red and blue, and is made, forinstance, of gelatine dyed with rhodamine, and the other half of thefilter is transparent for II and III yellow and green, but absorbent forI and IV, and is made, for instance, of gelatine dyed withnaphthol-green.

The relationship between the two-part filter and the iilm is moreclearly shown in Figs. 3 and 4. It is asumed that the rays from whitelight containing all colors are being passed through a filter upon a lm.In Fig. 3, lter 2a represents the filtering action of one-half of thetwo-colored lter referred to above, and is absorptive for the colors inranges II and III, but passes the colors of ranges I and IV. The lm iscomposed of sensitized layers 4 and 8 separated by a yellow filter layer6, which is absorptive of blue. Emulsion layer 4 is sensitized only forthe wave lengths of green and blue in ranges III and IV, and as only theblue and red rays can pass filter 2a, the layer 4 reacts only to theblue light. At the same time, filter 2a absorbs the yellow light ofrange III and passes onlythe red light through layer 4 to layer 8, whichis sensitized for the yellow and red wave lengths of ranges I and II.Filter layer 6 absorbs the light from range IV so that layer 8 isexposed to the red light only.

Fig. 4 shows the function of the other part of the two-part lter. Thishalf of filter 2b is absorptive for the colors red and blue in ranges Iand IV, respectively, and passes colors yellow and green in ranges IIand III. The film is the saine as in Fig. 3, but in this case, layer 4is exposed only to the green light of range III, while the layer 4 isexposed to the yellow light of range II.

The combined action of these two filter halves upon the exposing `of thelenticular film of this invention, is illustrated in Figs. 5 and 6.

In Fig. 5 the light rays coming from the object I8 pass through thetwo-color filter I2 having a portion transparent for red-bluecorresponding to lter 2a, Fig. 3, and a yellow-green portioncorresponding to filter 2b, Fig. 4, and are projected through lens I4onto the lens elements I5 of lenticular film I6.

'I'his film is similar to that shown in Figs. 3 and 4 and has twolight-sensitive layers 4 and 8 lying behind one another, and a filterlayer 6 arranged between them. The layer 4, lying next to the lenticularsurface, is sensitized for blue and green, while the layer 8 issensitized for red and yellow. Filter lays 6 is transparent only for redand yellow, so that it prevents the layer 8 from being exposed to bluerays.

Through the lens elements I5 of the lenticular surface, both halves offilter I2 are recorded at each picture spot side by side. Light comingfrom a red spot upon object I0 passes to the left half I8 of .thecorresponding spot in the layer l, while the right half 2II of thisspot, as Weil as both halves 22 and 24 of the corresponding spot in therst layer 4, remain unexposed.

After the film has been developed and the negative component images havebeen converted into colored positives, the colors of which arecomplementary to those which caused the negative images, the exposedhalf spot I8 will appear colorless, while the other half 20 of the samespot will turn out blue-green, and the entire corresponding spot in thelayer 4 will appear a yellowish-red.

After the dyestuii` has been washed out of the filter layer 6, the filmis projected by means of a white light in a projector provided with afilter similar to the filter I2. The light ray passing through the halfspots 2D and 24 lying behind one another and colored blue-green andyellowred, respectively, is entirely absorbed, while the light raypassing through the half spots I8 and 22 (the half spot I8 beingcolorless and the half spot 22 being yellow red) is coloredyellowish-red and is turned into pure red by being passed through thepart 2a of filter I2', which absorbs the yellow component.

Blue, green, or yellow spots of the object are recorded and reproducedin the same way subtractively, while spots of mixed color expose thecorresponding spots in both light-sensitive layers. After developingsuch a photographic picture, first the negative silver pictureconsisting of four coinponent pictures is obtained, and behind eacheinbossed lens there are, in pairs side by side and behind one another,the blackenings corresponding to the four different spectrum ranges.further treatment of the picture consists in converting the inseparablepicture layers into positive colored pictures, the layer recording theblue and green rays being turned into a positive picture in red-yellow,and the layer recording red and yellow rays being turned into a positivepicture in blue-green, and in washing out the dyestu from the lter layerso as vto make it transparent for all colors. The same mixed color willbe reproduced additively.

In Fig. 6 a three-color system is shown. The filter 30 has a red-bluezone 2c and a red-green zone 2d. The light-sensitive layer 4 of the filmis sentitized for blue and green, the layer 8 is sensitized for red,while the lter layer 6 is absorbent for blue and green.

Light from a red spot of the object exposes the whole corresponding spot32 in the layer 8', while both halves 34 and 36 of the correspondingspot in the layer 4 remain unimpressed. In the positive, therefore, thehalf spots 34 and 36 will be colored red, while the spot 32 will becolorless. In projecting, light rays penetrating these spots will becolored yellow but it will pass through both halves of the filter 30only red, as both halves of the lter are transparent for red, absorbingthe yellow component.

Light from a blue spot of the object exposes The the left half 34 of thecorresponding spot in the layer 4', while the right half 36 of thisspot, as well as the whole corresponding spot 32 in the layer 8' willremain unexposed. In the positive. therefore, the left half 24 of thespot in the layer 4' will appear colorless, while the right half 36 ofthis spot will be colored yellow-red, and the whole spot 32 in the layer8' will be colored bluegreen. In projecting, the light rays falling uponthe right half of spot 32 and the half spot 36 lying in front of itwilltherefore be wholly absorbed, while the light ray penetratingthrough the left half of spot 32 and the half spot 34 will be coloredblue-green, and as the right half of the iiller 30 is absorbent forgreen, a pure blue light will be emitted therefrom.

A green spot upon the object will be recorded and reproduced in the sameway subtractively, while yellow spots or spots of mixed color willexpose the corresponding spots in both lightsensitive layers to acertain extent, and consequently the same yellow or mixed color will bereproduced additively.

The conversion of the silver negatives into colored positives in allforms of the invention can be made according to any known method. Forinstance, both light-sensitive emulsions may contain leuco compounds. Inthis c-ase the twocolored positive pictures are produced at theoriginally unexposed spots by known methods. It is also possible toproduce stained color pictures; for this purpose it is advantageous touse a fine grained silver halogen emulsion for the lter layer, which haslittle light sensitiveness and causes very little light diffraction, inorder to effect chromium tanning of the filter layer containing silver,in a suitable phase of the operation to obtain a water-tight sealbetween the two picture layers, whereupon the production of theblue-green positive picture can be accomplished without disturbing thepreviously made and now water-tightly enclosed red-yellow positivepicture. In general, every method which can be used with inseparablepicture layers is suitable for producing subtractive two-color pictures,the -basic colors of which consist of the complementary parts of thevisible spectrum.

The described method has the following advantages as compared to othermethods:

a. More perfect color reproduction because of the use of at least fourspectrum ranges;

b. The complementary absorption spectra of the two subtractive layers donot interfere practically with one another, in contradistinction to theabsorptions with three subtractive layers;

c. A ne structure of the picture as compared to the known three-coloradditive method as here each vembossed lens has to produce the images ofonly two lter portions instead of three, and therefore the spaceoccupied by a picture element is correspondingly smaller;

d. Less light losses than with the known threecolor additive method ashere the projection filter weakens the light only by 50%, while thelight losses caused by three-color lters are considerably higher;

e. The diameter of the embossed lenses upon the lenticular film may besmaller than with the three-color method, since the picture elementconsists of only two components, consequently such a lrn can be madewith a finer grid, and the optical printing is m-ade easier.

Having now described a method by which the objects of this invention maybe obtained, what I claim is:

1. The method ofcolor photography which consists in exposing through atwo-color nlter,

light-sensitive layer lying behind itis sensitized; developing thenegative component images in said light-sensitive layers, and washingout the iilter layer between them; and converting each of the twonegative component images thus produced vinto a positive colored in thecolors for which the light-sensitive layer containing the other negativecomponent image was sensitized. Y

2. The method of color photography which consists in exposing through atwo-color lter, a lenticular nlm having two light-sensitive layerslyingbehind one another and which are sensitized for substantiallycomplementary colors, and a lter layer Ibetween them which istransparent only for the colors for which the light-sensitive layerlying behind it is sensitized; developing the negative component imagesin saidv light-sensitive layers, and washing out the iilter layerbetween them; converting each of the two negative component images thusproduced into a positive colored in the colors for which thelightsensitive layer containing the other negative component image wassensitized; and projecting the positive component images in their givenrelative position in the film through a iilter similar to that used intaking the pictures.

3. The method of color photography which consists in exposing through atwo-color iilter, a lenticular film having two light-sensitive layerslying behind one another. one of said layers being sensitized for colorslying within the short-wave part of the visible spectrum, the otherlayerbeing sensitized for colors lying within the longwave part thereof, anda filter layer between said light-sensitive layers which is transparentonly for the colors for which the light-sensitive layer lying behind itis sensitized; developing the negative component images in saidlight-sensitive layers, and washing out the filter layer between them;and converting each of the two negative component images thus producedinto a positive colored in the colors for which the other lightsensitivelayer was sensitized.

4. The method of color photography which consists in exposing through alter comprising a red-blue zone and a yellow-green zone, a lenticularfilm having two light-sensitive layers lying behind one another, one ofwhich is sensitized for blue and green, the other layer being sensitizedfor red and yellow, and a filter layer between said light-sensitivelayers which is transparent only for the colors for which thelight-sensitive layer lying behind it is sensitized; developing thenegative component images in said light-sensitive layers, and washingout the filter layer between them; and converting each of the twonegative component images thus produced into a positive colored in thecolors for which the other lightsensitive layer was sensitized.

5. The method.I of color photography which consists in exposing througha lter comprising a red-blue zone and a yellow-green zone, a. lenticularlm having two light-sensitive layers lying behind one another, the layerlying next to the lenticular surface being sensitized for blue andgreen. and the other layer being sensitized for red and yellow, and afilter layer between said light-sensitive layers which is transparentonly for red and yellow; developing the negative component images insaid light-sensitive layers, and washing out the lter layer betweenthem; and converting the negative component image in the iight-sensitivelayer arranged next to the lenticular surface into a positive colored inred-yellow, and the negative component image in the otherlight-sensitive layer into a positive colored in blue-green. V

6. The method of color photography which consists in exposing through afilter comprising a red-blue zone and a red-green zone, a. lenticularfilm havingv two light-sensitive layers lying behind one another, one ofwhich is sensitized for blue and green, and the other layer beingsensitized for red, and a filter layer between said lightsensitivelayers which is transparent only for the colors for which thelight-sensitive layer lying behind it is sensitized; developing thenegative component' images ln said light-sensitive layers, and washingout the lter layer between them; and converting each of the two negativecomponent images then produced into a positive colored in the colors forwhich the other lightsensitive layer was sensitized.

7. The method of color photography which consists in exposing through afilter comprising a red-blue zone and a red-green zone, a lenticular lmhaving two light-sensitive layers lying behind one another, the layerlying next to the lenticular surface being sensitized for blue andgreen, and the other layer being sensitized for red, and a lter layerbetween said light-sensitive layers which is transparent only for red;developing the negative component images in said lightsensitive layers,and washing out the lter layer between them; and converting the negativecomponent image in the light sensitive layer arranged next to thelenticular surface into a positive co1- ored in red, and the negativecomponent image in the other light-sensitive layer into a positivecolored in blue-green.

HANS KUDAR.

